Use of computed tomography (CT) to assess the amount of calcified
plaque in the coronary arteries is accepted as an alternative to
catheterization in patients at low-to-intermediate risk for coronary
artery disease (CAD) who present with chest pain. It is also becoming an
increasingly popular method for routine CAD screening in asymptomatic
patients as part of a comprehensive risk assessment. But a study in the
July 13 Archives of Internal Medicine concluded that widespread use of
this technology could dramatically increase the number of
radiation-induced cancer cases in the U.S., with women especially at
risk.

How the study was performed

The authors estimated the radiation doses from various protocols
utilized in published clinical studies of coronary CT angiography (CCTA)
and applied these estimates to radiation risk models to obtain the
excess lifetime risk of radiation-induced cancer. They concluded that if
50 million healthy Americans--the number proposed by Screening for Heart
Attack Prevention and Education guidelines--undergo a single screening
with a medium dose of radiation, an additional 5,600 cases of
radiation-induced cancer would occur. Screening every tive years would
increase the excess cancer risk by 62 per 100,000 women and 42 cases per
100,000 men.

Women and risk

In January 2009, Women's Heart Advisor ran a story on this
subject before the risks of excess cancer were known. Cleveland Clinic
cardiovascular imaging specialist Ronan Curtin, MD, expressed concern
that CCTA could cause long-term increased risk of breast and lung
cancer, because these organs readily absorb radiation. Rapid cell
turnover increases the chance that developing cells will mutate, causing
cancer.

Because such changes would produce slow-growing cancers, the
lifetime risk decreases with age, Dr. Curtin said. A study reported in
the July 18, 2007, Journal of the American Medical Association found the
increased lifetime estimated risk of developing cancer following a CCTA
study was i in 143 for a 20-year-old woman and i in 715 for a
60-year-old woman--a sufficient difference that "extra caution
should be exercised before ordering this test for women in their 20s to
40s," he said.

More studies needed

Part of the problem may lie in the absence of a standardized
screening protocol. In the Archives study, a 10-fold difference in the
amount of radiation delivered during CCTA was seen, even when the tests
were performed on identical machines in different hospitals.
Establishing a safe dose of radiation for the test would minimize cancer
risk. Additionally, further studies need to be done to confirm the
benefits of CCTA. Until these issues are addressed, the potential
cancer-causing risks of the technology should be balanced with its
potential benefits.

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DR. CHO'S VIEW ...

It is crucial for patients to understand that radiation risk exists
not only with coronary CT, but with other cardiac tests as well. Nuclear
stress tests expose patients to high levels of radiation. Cardiac
catheterization may also give patients a moderate radiation dose,
depending on the length of the procedure. For younger patients, I
typically tend to favor stress echocardiography, since the
ultrasound-based technology emits no radiation.

For any test, it is important to weigh the risks and the benefits.
If you are concerned about the radiation risk, talk to your doctor. At
Cleveland Clinic, we use several sophisticated dose-limiting protocols
for coronary CT that we helped to develop. For example, instead of
leaving the X-ray tube on continuously while the scanner revolves around
the patient, we can turn the X-ray tube on only during short intervals
of the patient's heartbeat. This reduces X-ray exposure by 50 to 75
percent, to a level similar to that of cardiac catheterization.